30 Jul
2010
30 Jul
'10
2:01 p.m.
On Friday 30 July 2010 19:23:00, Brent Yorgey wrote:
If I understand correctly, however, there is some debate over what the "correct" laws for MonadPlus ought to be.
Yes, and the haskellwiki page on MonadPlus doesn't even mention the 'right zero' property (but the Control.Monad haddocks do).
One can also imagine other useful monads which satisfy other MonadPlus laws but not the one above, such as MaybeT (State Int), in which failure short-circuits any future modifications to the state, but does not roll back any state modifications that may have happened up to the point of failure.
-Brent
Yep, there are several useful variants possible. That is probably why there's no final agreement on the laws.